This application claims the priority of Korean Patent Application No. 2002-78169, filed on Dec. 10, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a field emission device, and more particularly, to a field emission device using carbon nanotubes (CNTs).
2. Description of the Related Art
Carbon nanotubes (CNTs), by which field emission is performed even at a very low voltage due to their small diameter and pointed tube, are similar to fulleren (C60). Since they have an excellent electron emission characteristic and chemical and mechanical durability, their physical properties and applications have steadily been studied. A Spindt-type (U.S. Pat. No. 3,789,471) field emission emitter, which is generally used for field emission displays, uses a micro-tip as an emitter for emitting electrons. The emitter has a problem in that the life span of a micro-tip is shortened due to atmospheric gases or a non-uniform field during a field emission operation. In addition, with such a conventional metal emitter, a work function must be decreased to decrease a driving voltage for field emission, but there are limitations. To overcome this problem, field emission arrays using carbon nanotubes which have a substantially high aspect ratio, excellent durability due to their structure being similar to that of C60, and excellent electron conductivity, as an electron emission source, have been studied.
FIG. 1 schematically illustrates the sectional structure of a CNT electron gun of a conventional field emission array having one gate electrode which is disclosed in U.S. Pat. No. 6,440,761.
A cathode 2 is formed on a substrate 1, and a cathode insulating layer 3 that has an opening 3a which covers part of the cathode 2 and through which the center of the cathode 2 is exposed, is formed on the cathode 2. A gate insulating layer 4 and a gate electrode 5 which have a through hole 4a and a gate hole 5a, respectively, larger than the opening 3a of the cathode insulating layer 3, are formed on the cathode insulating layer 3. Meanwhile, grown or coated CNT emitters 8 are provided on the top of the cathode 2. In FIG. 1, reference numerals 9, 9b, and 9c denote a front substrate, an anode, and a phosphor layer, respectively.
FIG. 2 schematically illustrates the sectional structure of a CNT electron gun of a conventional field emission array having two gate electrodes. The electron gun has a structure in which a second gate insulting layer 6 and a second gate electrode 7 on the second gate insulating layer 6 are added to the electron gun shown in FIG. 1. Specifically, a first gate insulting layer 4 and a first gate electrode 5 which have a through hole 4a and a first gate hole 5a, respectively, larger than the opening 3a of the cathode insulating layer 3, are formed on the cathode insulating layer 3. The second gate insulting layer 6 and the second gate electrode 7 which have a through hole 6a and a second gate hole 7a, respectively, greater than the first gate hole 5a of the first gate electrode 5, are formed on the first gate electrode 5. Meanwhile, grown or coated CNT emitters 8 are provided on the top of the cathode 2.
The field emission device having the structure shown in FIG. 2, unlike the field emission device shown in FIG. 1, has two gate electrodes, i.e., first and second gate electrodes, thereby performing electron control such as prevention of internal arcing and effective focusing. FIG. 3 is a plan photograph showing the structure of a conventional field emission device having four electron guns arranged in one pixel and illustrates the shape and relation of the CNT emitters 8 and openings 8 and 6a of a gate electrode of the conventional CNT field emission device.
A field emission device using a CNT electron gun, unlike a field emission device using Spindt-type micro-tips, emits electrons from most CNTs of most CNT emitters on a cathode, and thus has a high current density. On the other hand, electrons emitted over wider range can reach the phosphor in unintended areas. Thus, if the field emission device using CNTs as an electron emission material cannot effectively control electrons emitted from CNTs, color purity and luminance may be lowered.
Also, each electron gun of the conventional field emission device corresponds to one pixel and includes CNT emitters formed in a circular shape and openings 5a and 6a of a gate electrode having a circular shape corresponding to the CNT emitters, as shown in FIG. 4. Electrons are uniformly dispersed in all directions from each electron gun such that emitted electrons reach the phosphor in neighboring, unintended areas as described above, and color purity and luminance is further lowered.
Likewise, in a field emission device having a structure in which a plurality of electron guns corresponding to one pixel are provided, in order to obtain good picture quality, electrons emitted from each electron gun should converge on an intended area of the phosphor and not on any other area.